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Calcitonin

Calcitonin is a 32 amino acid polypeptide hormone that is produced in humans primarily by the C cells of the thyroid, and in many other animals in the ultimobranchial body. more...

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Synthesis

It is formed by proteolytic cleavage of a larger prepropeptide which is the product of the CALC1 gene, which itself is part of a superfamily of related protein hormone precusors including Islet Amyloid Precursor Protein, Calcitonin Gene-Related Peptide and the precursor of Adrenomedullin.

Physiology

The hormone participates in calcium and phosphorus metabolism and it was found in fish, reptiles, birds and mammals. Most evidence points to that Calcitonin is not of physiological importance to humans, except for it's pharmacological use (see below).

Specifically, calcitonin reduces blood calcium levels in three ways:

Decreasing calcium absorption by the intestines
Decreasing osteoclast activity in bones
Decreasing calcium and phosphate reabsorption by the kidney tubules

Its actions, broadly, are:

Bone mineral metabolism
- Prevent postprandial hypercalcemia resulting from absorption of Ca++ from foods during a meal
- Promote mineralization of skeletal bone
- Protect against Ca++ loss from skeleton during periods of Ca++ stress such as pregnancy and lactation
Vitamin D regulation
A satiety hormone
- Inhibit food intake in rats and monkeys
- May have CNS action involving the regulation of feeding and appetite

Like the PTH receptor, the receptor of calcitonin is a serpentine G protein-coupled receptor with seven membrane spanning regions which is coupled by Gs to adenylyl cyclase and thereby to the generation of cAMP in target cells. Indeed, the PTH and calcitonin receptors are family members which are related in amino acid sequence, though their ligands are not.

Pharmacology

Salmon calcitonin is used for the treatment of:

Postmenopausal osteoporosis
Hypercalcaemia
Paget's disease
Bone metastases

History

Calcitonin was purified in 1962 by Copp and Cheney. While it was initially considered a secretion of the parathyroid glands, it was later identified as the secretion of the C-cells (parafollicular cells) of the thyroid.

Read more at Wikipedia.org

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Fracture healing in normal and hypogonadal male rats after salmon calcitonin administration
From Journal of Bone and Joint Surgery, 1/1/03 by Koulouris, I Ch

Purpose: The study was conducted to evaluate the effect of salmon calcitonin (sCT) on fracture healing in normal and hypogonadal male rats.

Material and Method: Fifty six male Wistar rats, aged 3 months, were undertaken hemiosteotomy of the distal femur shaft, of standard length and width. Half of the animals had been orchiectomised at the age of 2 months. The animals were divided in 8 groups, 7 rats each, as follow: A, a (normal, no sCT), B, b (normal+Sct), C,c(orchiectomised) and D,d (orchiectomised+Sct). Salmon calcitonin was administered immediately after the hemiosteotomy in a dose of 5IU/day subcutaneuusly. Groups A, a, C and c were given placebo. The animals of the groups a b, c, and d were killed at 2 weeks, while the animals of the groups A, B, C, and D were killed at 4 weeks. After the euthanasia, total bone density and cortical bone density of the callus was estimated by peripheral quantitative computed tomography (pQCT). Histological and histomorfometric parameters of the callus were estimated as well.

Results: The mean cortical bone density was 1221.93±13.82(g/cm^sup 3^±SE) for the group a, 1281.3±13.57 for b, 1221.41±18.24 for c, 1245±17.12 for d, 1173.45±34.14 for A, 1298.9±11 for B, 1280.78±13.68 for C, and 1279.4U19.2 for D. The mean total bone density was 843.95±13.69 (g/cm^sup 3^±SE) for the group a, 859.84±26.46 for b, 892.27±25.3 fore, 861.37±10.88 for d, 818.97±32.5 for A, 926.39±19.6 for B, 888.31±24.19 for C, and 912.75±28.13 for D. Values of cortical bone density in group b and B were significantly greater than a and A, respectively (b>a, p=0.01 and B>A, p=0.002). Total bone density of the callus was statistically greater in group B than A (B>A, p=0.01). According to the histological and histomorphometric results, sCT increased the amount of cartilage (p=0.014) and the amount of woven bone (p=0.015) in group b compared to a, while osteoblasts number showed no difference between the two groups. Comparing groups c and d, sCT increased the amount of cartilage (p=0.036) and the amount of woven bone (p=0.0014) in group d compared to c, while decreased osteoblasts number in group d (p=0.03). In four weeks the amount of cartilage is significant greater in group D versus C (p=0.006). as well as the amount of woven bone (p=0.0004). The size of the callus is significant greater in group D compared to C as well (p=0.052).

Conclusion: It appears that salmon calcitonin administration improves significantly the parameters of callus bone density in normal rats and increases the amount of cartilaginous callus and woven bone both in normal and orchiectomised rats.

I.Ch. Koulouris, I. Dontas, I. Paspati, L. Khaldi, P. Raptou, A. Galanos, G.P. Lyritis.

Laboratory for the Research of Musculoskeletal System, Kifisia.

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